Preliminary studies on the cat in this laboratory have shown that conditioning effects on sensory input from the trigeminal and upper cervical roots can be demonstrated from ulnar and radial nerves and to a lesser extent from median and tibioperoneal nerves. Acupuncture stimulation delivered to the first dorsal interosseous interspace has also been shown to produce depression of conduction of input through the spinal trigeminal nucleus which lasts for periods of twenty minutes after cessation of the acupuncture stimulation. The latter effects are obtained in only 25% of experiments and are thus quite unpredictable. Experiments are described to attempt to clarify the mechanisms involved and to try to decrease or eliminate the marked variability of the acupuncture effects. The significance of these studies is primarily in terms of an effort to determime whether a scientific basis can be established for acupuncture analgesia and if so, such information would lead to considerable re-evaluation of our concepts of pain mechanisms.